Is Telomere Length a Biomarker of Adaptive Response in Space? Curious Findings from NASA and Residents of High Background Radiation Areas

Shortened telomere length in peripheral blood leukocytes is associated with cumulative radioactive iodine doses in patients with differentiated thyroid carcinoma

BACKGROUND

Telomere length is associated with cancer risk and cancer aggressiveness. Radioactive iodine (RAI) therapy for thyroid cancer has raised concerns for second primary malignancy (SPM) in patients with high cumulative doses. The association between RAI dose and peripheral blood leukocyte telomere length was examined.

METHODS

A total of 425 patients were included who underwent total thyroidectomy and were followed up for at least 1 year with or without RAI treatment. The relative telomere length (RTL) of the patients was assessed via a quantitative polymerase chain reaction amplification method. RAI doses were divided into five groups on the basis of cumulative dose, and a comparison was made among these groups.

RESULTS

The number of patients with RAI treatment was 287 (67.5%), and the cumulative RAI dose was 3.33 GBq (range, 1.11-131.35 GBq). The mean RTL was significantly shorter in the highest RAI group (>22.2 GBq) compared to both the no-RAI and lower dose groups. The association between RAI dose and RTL was positive in the lower RAI group (1.1-3.7 GBq) and negative in the highest RAI group in both univariate and multivariate analyses. We observed 59 (13.9%) SPMs and 20 (4.7%) mortalities, and RTL did not show a significant risk effect for all-cause, thyroid cancer-specific, or SPM-specific mortality.

CONCLUSIONS

In patients with thyroid cancer who underwent total thyroidectomy, peripheral blood leukocyte telomere length exhibited a significant association with cumulative RAI dose higher than 22.2 GBq. These results suggest the possibility of telomere length shortening in patients who undergo high-dose RAI treatment.

How the adaptation of the human microbiome to harsh space environment can determine the chances of success for a space mission to Mars and beyond

The ability of human cells to adapt to space radiation is essential for the well-being of astronauts during long-distance space expeditions, such as voyages to Mars or other deep space destinations. However, the adaptation of the microbiomes should not be overlooked. Microorganisms inside an astronaut's body, or inside the space station or other spacecraft, will also be exposed to radiation, which may induce resistance to antibiotics, UV, heat, desiccation, and other life-threatening factors. Therefore, it is essential to consider the potential effects of radiation not only on humans but also on their microbiomes to develop effective risk reduction strategies for space missions. Studying the human microbiome in space missions can have several potential benefits, including but not limited to a better understanding of the major effects space travel has on human health, developing new technologies for monitoring health and developing new radiation therapies and treatments. While radioadaptive response in astronauts' cells can lead to resistance against high levels of space radiation, radioadaptive response in their microbiome can lead to resistance against UV, heat, desiccation, antibiotics, and radiation. As astronauts and their microbiomes compete to adapt to the space environment. The microorganisms may emerge as the winners, leading to life-threatening situations due to lethal infections. Therefore, understanding the magnitude of the adaptation of microorganisms before launching a space mission is crucial to be able to develop effective strategies to mitigate the risks associated with radiation exposure. Ensuring the safety and well-being of astronauts during long-duration space missions and minimizing the risks linked with radiation exposure can be achieved by adopting this approach.

Exposure of Shewanella oneidensis MR-1 to Sublethal Doses of Ionizing Radiation Triggers Short-Term SOS Activation and Longer-Term Prophage Activation

Currently, there is a lack of bacterial biomarkers indicative of exposure to ionizing radiation (IR). IR biomarkers have applications for medical treatment planning, population exposure surveillance, and IR sensitivity studies. In this study, we compared the utility of signals originating from prophages and the SOS regulon as biomarkers of IR exposure in the radiosensitive bacterium Shewanella oneidensis. Using RNA sequencing, we demonstrated that 60 min after exposure to acute doses of IR (40, 1, 0.5, and 0.25 Gy), the transcriptional activation of the SOS regulon and the lytic cycle of the T-even lysogenic prophage So Lambda are comparable. Using quantitative PCR (qPCR), we showed that 300 min after exposure to doses as low as 0.25 Gy, the fold change of transcriptional activation of the So Lambda lytic cycle surpassed that of the SOS regulon. We observed an increase in cell size (a phenotype of SOS activation) and plaque production (a phenotype of prophage maturation) 300 min after doses as low as 1 Gy. While the transcriptional responses of the SOS and So Lambda regulons have been examined in S. oneidensis after lethal IR exposures, the potential of these (and other transcriptome-wide) responses as biomarkers of sublethal levels of IR (<10 Gy) and the longer-term activity of these two regulons have not been investigated. A major finding is that after exposure to sublethal doses of IR, the most upregulated transcripts are associated with a prophage regulon and not with a DNA damage response. Our findings suggest that prophage lytic cycle genes are a promising source of biomarkers of sublethal DNA damage. IMPORTANCE The bacterial minimum threshold of sensitivity to ionizing radiation (IR) is poorly understood, which hinders our understanding of how living systems recover from the doses of IR experienced in medical, industrial, and off-world environments. Using a transcriptome-wide approach, we studied how in the highly radiosensitive bacterium S. oneidensis, genes (including the SOS regulon and the So Lambda prophage) are activated after exposure to low doses of IR. We found that 300 min after exposure to doses as low as 0.25 Gy, genes within the So Lambda regulon remained upregulated. As this is the first transcriptome-wide study of how bacteria respond to acute sublethal doses of IR, these findings serve as a benchmark for future bacterial IR sensitivity studies. This is the first work to highlight the utility of prophages as biomarkers of exposure to very low (i.e., sublethal) doses of IR and to examine the longer-term impacts of sublethal IR exposure on bacteria.

Biological Protection in Deep Space Missions

During deep space missions, astronauts are exposed to highly ionizing radiation, incl. neutrons, protons and heavy ions from galactic cosmic rays (GCR), solar wind (SW) and solar energetic particles (SEP). This increase the risks for cancerogenisis, damages in central nervous system (CNS), cardiovascular diseases, etc. Large SEP events can even cause acute radiation syndrome (ARS). Long term manned deep space missions will therefor require unique radiation protection strategies. Since it has been shown that physical shielding alone is not sufficient, this paper propose pre-flight screening of the aspirants for evaluation of their level of adaptive responses. Methods for boosting their immune system, should also be further investigated, and the possibility of using radiation effect modulators are discussed. In this paper, especially, the use of vitamin C as a promising non-toxic, cost-effective, easily available radiation mitigator (which can be used hours after irradiation), is described. Although it has previously been shown that vitamin C can decrease radiation-induced chromosomal damage in rodents, it must be further investigated before any conclusions about its radiation mitigating properties in humans can be concluded.

Be cool to be far: Exploiting hibernation for space exploration

In mammals, torpor/hibernation is a state that is characterized by an active reduction in metabolic rate followed by a progressive decrease in body temperature. Torpor was successfully mimicked in non-hibernators by inhibiting the activity of neurons within the brainstem region of the Raphe Pallidus, or by activating the adenosine A1 receptors in the brain. This state, called synthetic torpor, may be exploited for many medical applications, and for space exploration, providing many benefits for biological adaptation to the space environment, among which an enhanced protection from cosmic rays. As regards the use of synthetic torpor in space, to fully evaluate the degree of physiological advantage provided by this state, it is strongly advisable to move from Earth-based experiments to 'in the field' tests, possibly on board the International Space Station.

Space Medicine: Why Do Recently Published Papers about Telomere Length Alterations Increase our Uncertainty Rather than Reduce it?

There is a growing interest in examining alterations in telomere length as a reliable biomarker of general health, as well as a marker for predicting later morbidity and mortality. Substantial evidence shows that telomere length is associated with aging; telomere shortening acts as a "counting mechanism" that drives replicative senescence by limiting the mitotic potential of normal (but not malignant) cells. In this Correspondence, we attempt to answer the question of why recently published papers about telomere length alterations increase our uncertainty rather than reduce it. This discussion includes three major research areas regarding telomere length: environmental stressors, aging, and life span. Our review suggests that activation of telomerase activity due to stressors in space might be a double-edged sword with both favorable and unfavorable consequences. The selection of an effect's consequence must clearly elucidate the experimental conditions as well as associated stressors. In this Correspondence, we attempt to answer the question of why recently published papers about telomere length alterations increase our uncertainty rather than reduce it. The selection of an effect's consequence must clearly elucidate the experimental conditions as well as associated stressors. Both positive and negative consequences must be clearly addressed in order to bolster the conclusions, as well as identify future research directions.

A Longitudinal Epigenetic Aging and Leukocyte Analysis of Simulated Space Travel: The Mars-500 Mission

Astronauts undertaking long-duration space missions may be vulnerable to unique stressors that can impact human aging. Nevertheless, few studies have examined the relationship of mission duration with DNA-methylation-based biomarkers of aging in astronauts. Using data from the six participants of the Mars-500 mission, a high-fidelity 520-day ground simulation experiment, we tested relationships of mission duration with five longitudinally measured blood DNA-methylation-based metrics: DNAmGrimAge, DNAmPhenoAge, DNA-methylation-based estimator of telomere length (DNAmTL), mitotic divisions (epigenetic mitotic clock [epiTOC2]), and pace of aging (PoA). We provide evidence that, relative to baseline, mission duration was associated with significant decreases in epigenetic aging. However, only decreases in DNAmPhenoAge remained significant 7 days post-mission. We also observed significant changes in estimated proportions of plasmablasts, CD4T, CD8 naive, and natural killer (NK) cells. Only decreases in NK cells remained significant post-mission. If confirmed more broadly, these findings contribute insights to improve the understanding of the biological aging implications for individuals experiencing long-duration space travel.

Long-duration space travel is marked by a unique combination of stressors known to impact human aging. Using data from six participants of the Mars-500 mission, a high-fidelity 520-day ground simulation experiment, Nwanaji-Enwerem et al. report significant associations of mission duration with decreased biological aging measured via blood DNA methylation.